Hydraulic packing



Dec. 20, 1955 R. E. sNYDl-:R 2,72 7,797

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United States Patent() HYDRAULIC PACKING VRobert E. Snyder, Pasadena, Calif.

Application June 16, 1951, Serial No. 232,035 2 Claims. (Cl. 309-22) My invention relates generally to the art of hydraulic packing, and more particularly, to a self-sealing hydraulic packer for reciprocating movement with respect to a wall of the packer recess. v A

In hydraulic packers of the type which employ a rounded edge to engage a wall of the packer recess and which further are compressible by the hydraulic fluid pressure to form a tight seal against leakage of said iluid along both walls of the packer recess, similar for example to an O-ring type packer, the major problem is to prevent damage to or destruction of the packer during reciprocating motion between the respective walls of the recess. In static seals where neither wall of the recess moves with respect to the other wall, there is no damage to the packer due to motion, but Where one wall of the recess moves with respect to the other wall, either by rotating, by reciprocating, or by a combination of both, various types of damage to the packer occur. Further, if, in addition to motion, the packer is subjected to substantial hydrostatic pressure, the damage to the packer becomes still more severe in that the hydraulic pressure tends to extrude the packer material out of the packer recess.

It is common practice where both high pressures and motion are anticipated to provide O-ring packers with leather, ber, micarte, etc., backer rings positioned within the O-ring groove and upon either side of the O-ring to prevent extrusion of the O-ring packing material into the interstice between the moving walls under the impress of hydraulic pressure and/ or movement of one of the packer recess Walls. Quite a variety of such combinations are to be found in the prior art, but while some of these are benecial to prevent extrusion, they do not provide protection for the packer against rotation and shear of the packer within the groove. In long-stroke pistons, the danger of rotational shear of the O-ring packer has proven so great as to actually eliminate their use in such installations in spite of the otherwise high packing efficiency.

It is therefore a major object of this invention to provide means to prevent physical damage to the packer due to rotation within the recess or groove during its operational life.

In reciprocatory movement between two concentric parts, there is often substantial clearance between the parts to insure free movement. The actual dimensional limits of this clearance are determined by the prerequisites of the device in which the reciprocatory movement is desired. In hydraulic systems, the packer must bridge and seal this clearance. In many devices, it has been found that under certain operating conditions, one of the moving parts will move out of the desired axial concentricity with respect to the other so that the clearance will be concen trated on one side of the unit while on the opposite side, the clearance will be practically zero, and a metal-to-metal engagement will result. In thisy case, the mechanical radial pressure between the packer and the recess walls will be high on the side where there is minimum clearance and low on the side of maximum clearance.

It is therefore a second object of the invention to prolee vide a simple means to maintain concentricity between the reciprocating parts to thereby equalize the mechanical load upon all parts of both the packer and the backer rings.

In long-stroke reciprocating hydraulic parts, such as a cylinder and piston where the stroke is many times the diameter of the piston, it has been found that O-ring packers tend to roll unequally due to high and low clearances on opposite sides, and that this will cause the O-ring to twist about its circumferential axis and to tear or shear apart. i

It is therefore another object of the present invention to provide a packer having a shape that will prevent'it from rolling in its groove, and being damaged thereby, 4

while still retaining the valuable rounded inner and outer faces of the packer which seal against the inner and outer walls respectively, of the packer recess.

In a piston packer assembly, it is necessary to mechanically deform the packer on the piston where it is inserted into the cylinder in order to make the packer seal by its inherent resiliency against both the piston on the inside and the cylinder wall on the outside. In the trade, such deformation of the packer is referred to as ,squeezef It is common practice to assume that the piston may be positioned non-concentrically in the cylinder land hence the packer is initially squeezed enough that it will seal even though the piston were to be moved as far as possible out of concentricity with the cylinder, i. e., actually to contact one side of the cylinder. Thus, the initial squeeze on the packer is greater than would be necessary should the piston be held at all times axially' concentric in the cylinder. The friction of such a highly squeezed packer is much greater than necessary for a leakless seal. Both the squeeze and vthe resultant friction may be held to a minimum if the piston is held axially concentric in the cylinder. It is further to be noted that metal-to-metal contact between a piston and the cylinder wall in the absence of a lubricant or in the presence of a-non-lubricant iluid, will often cause the piston and the cylinder to gall and to destroy each other. But, if the piston is held concentric with the cylinder, such possibility is minimized.

A further object of the present invention is to provide a packer assembly having means therein to hold the piston concentric within the Cylinder, and thereby minimize the friction of the packers against movement of the piston as wg as prevent galling of the piston against the cylinder w In packers having minimum squeeze against the cylinder wall, there is a tendency for dirt to ride past the packer and in so doing, to damage the packer and break the seal, as well as to cause the piston to gall against the cylinder.

It is therefore another object to providea means inl conjunction with the seal, to wipe foreign matter from the cylinder wall in advance of the seal ring itself in either one or in both directions of movement, and 'thereby protect the seal from damage and the piston-cylinder assembly from galling.

A further object is to provide a simple, rugged, and practical packer which can t into standard packer grooves, which will be easily serviceable, have a long life, be reasonable in cost, and which will seal over a very wide range of'pressures.

These and other objects and advantages of this invention will be apparent from a consideration of the following specification, read in connection with the accompanyv ing drawings, wherein:

Figure 2 is a fragmentary cross-section of the piston taken along the lines 2-2 of Figure l; and

Figure 3 is a cross-section of the packer sealing ring.

Figure l shows a vertical cross-section of a free piston type hydropneumatic accumulator which illustrates one use of the packer system of the present invention. The packer system is equally adaptable to other types of pistons, as well as to rod pack-ois and other types of reciprocating seals. The description of the packer in the accumulator as shown in Figure 1, will show the details of one form of a preferred structure. lts adaptation to other types of seals wherein reciprocal movement is inherent will be readily understood by those versed in the art.

The accumulator is comprised essentially of three parts, a base 11, a tubular body 12, and a piston 13. The base 11 of cast metal has a bore 14 extending completely therethrough and is provided with a conventional iange 15 on the lower end, adapted to be connected into a hydraulic system or other liquid conveyor, and with a v second ange 16 at its upper end. The tubular body 12 is comprised essentially of a metal tube 12a having a ange 17 affixed as by welding to the lower end of the body 12. The ilange 17 is complementally faced to that of base ange 16. These two flanges are bolted together by capscrews 1S in the conventional manner with gasket 19 sealing the joint between them.

A boss 2d upon base 11 extends above ilange 16 into the bore 21 of flange 17 and its upper face 22 is flat and perpendicular to the axis of base 11. This face 22 also serves as a stop for piston 13 at the lowermost point of its travel.

The upper end of the tubular body 12 is closed with a plug 25 welded into the tube. Plug 25 has an inner face 26 which is flat and perpendicular to the axis of the body 12 and which further serves as a stop for piston 13 at the uppermost point of its travel. Plug 25 is further provided with port 2'7 which is connected to pipe 28, pressure gauge 29 and shut-off valve 30, through which gas may be put into the accumulator 10.

The inner surface of tubular body 12 is bored, honed, hard chrome plated, and polished to present a hard smooth cylindrical surface upon which piston 13 may ride. The hydropneumatic unit 10 thus provides two dependeutly variable chambers, chamber 36 above the piston, and chamber 37 below the piston. The upper chamber 36 is iilled with gas under pressure from the pipe 2S and the lower chamber is lled with fluid from the line. The packing used on piston 13 serves to isolate chambers 36 and 37, and to prevent the admixture or leakage of either the gas or the uid from their respective chambers 36 and 37 into the other across piston 13.

In a hydropneumatic unit of the type shown in Figure l, as well as in many other types of hydraulic units, the pressures in chambers 36 and 37 may vary over wide ranges. 1f, for example, the gas precharge in chamber 36 be set at 500 p. s. i., and the liquid preessure in chamber 37 be nearly zero, the pressure across the packing will be substantially 500 p. s. i., and the piston 13 will rest against the lower stop 22 in its extreme downward position. Now, if the fluid pressure increases up to 500 p. s. i., the pressure differential across the packers will decrease down to Zero when the fluid pressure reaches 500 p. s. i.

It the line pressure is further increased above 500 p. s. i. to, tor example, 600 p. s. i., the piston 13 will move upwardly, compressing the gas in chamber 36 according to the well-known gas laws wherein P1V1=P2V2- When the gas pressure reaches 6G() p. s. i., the piston will stop its motion and the pressure differential across the packers will again be substantially zero. in order to be maximurnly etlective, the packing must seal at near zero pressure differentials against creep or capillary leakage as well as against whatever maximum pressure differential the operation of the system might require. 1t is 4 also necessary that the triction of the packers against the cylinder walls be at the very minimum for smooth movement of the piston in response to small changes in the line fluid pressure.

Turning now to Figure 2 of the drawings, piston 13 is comprised essentially of a tubular body 5t) having its lower end 51 closed to formthe bottom or head of the piston. The piston 13 is of cast metal and is htollow with its bore 52 open at the upper end or skirt 53 much like a conventional gasoline engine piston. In the accumulator 10, as shown in Figure l, the piston 13 is positioned with the skirt 53 facing upwardly toward plug 25 of tubular body 12, and with the head 51 facing downwardly toward the base 11. The lower face 54 of head 51 is flat and normal to the axis of the piston, and is further adapted to rest against the stop face 22 of base 11 when in the extreme downwardly position. ln a similar manner, the upper face 55 of the skirt 53 of the piston is also llat and normal to the axis of the piston and is likewise adapted'to rest against the stop tace 26 of plug 25 when in the extreme upwardly position.

The outer circumferential surface of piston 13 is divided into two sections, the skirt section 61 and the head section 62, having an undercut central section 63 which provides a substantial annular pocket 64 between the outside of the piston and the bore 35 of the tubular body 12. Between the head section 62 and the head end 51 of the piston 13 is cutback portion 65 having a at shoulder 66 directly abutting head section 62. A wiper ring 7i) of leather or other suitable material is seated against shoulder 66 and is held loosely in position by a keeper ring '71 which is in turn held by snap ring 72 lodged in a groove '73 in head 51 of piston 13 just above lower face 54 on the outback portion 65. Wiper ring 70 iits snugly but not necessarily in fluid-tight engagement with portion and keeper ring 71 has enough clearance 74 between its bore and the outer face of portion 65 for easy assembly. This wiper ring is not designedto hold pressure and fluid leakage around it is desirable. It is solely used to wipe dirt and other fluid-born matter oli of the wall 35 of tubular body 12 so that such material will not come in contact with the packer seal ring 40.

Both skirt section 61 and head section 62 on the outside piston 13 are provided with a pair of parallel circumterential grooves 80 and 81. In grooves 80 are positioned the two split guide rings 82. These rings, made preferably of micarta or a similar wear-resistant inert material, serve to hold the piston 13 centralized in the bore of tubular body 12. They are cut to close tolerance and tit the bore snugly while they seat solidly against the bottorn 84 of their respective grooves 80. The outside diameter of these guide rings 82 is enough greater than the outside diameter of sections 61 and 62 of piston 13 that the metal portion of the piston never makes metal-tometal contact with the walls 35 of tubular body 12. Experience has shown that when such Contact does exist in the presence of many liquids having little or no lubricant qualities that severe galling action will take place, and that the piston often becomes completely jammed in the cylinder. In addition to this, any abrasion or galling or other damage to the surface 35 of tubular body 12 immediately renders the seal ring 40 inoperative by allowing leakage past the seal as well as by actually cutting and destroying the packing ring 40. Guide rings 82, by eliminating all metal-to-rnetal engagement between the piston 13 and the cylinder 12, entirely eliminate such a possibility. The additional action of the Wiper ring prevents the entry of metallic chips or detritus which might bridge the gap between the piston surface 60 and the wall 35 maintained by the guide rings 82.

By reference to Figures 2 and 3 of the drawings, the details of the packer assembly and the sealing ring may be seen. The sealing Vring 40 is made of rubber, synthetic rubber, or one of the plastic materials which is both resilient and suitable for the temperature range and the uid to be contained. As may be seen best in Figure `3, the ring 40 is approximately rectangular in cross-section, but has a radially arcuate form on both its outer circumference 41 and its inner circumference 42. The upper and lower sides 43 and 44, respectively, of the ring 40 are f flat, parallel and normal to the axis of the ring. The

arcuate inner and outer faces 42 and 41, respectively, blend into the at sides with smooth small curved corners 45, 46, 47 and 48 so that there are no sharp edges to become scutfed or to start a tear into the main body of the ring 40. The ring may be molded in one piece using standard rubber molding techniques as already well known to the art. The ilash from the molding process is cut'or ground oif in the usual manner. The dimensions of the ring follow closely those for standard O-rings in their inside and outside diameters, the arcuate faces 41 and 42 having the same radius. However, the axial thickness of the ring between the at faces 43 and 44 is less than the distance between arcuate faces 41 andA 42 for reasons which shall hereinafter be explained.

Each groove 81 has positioned therein a complete set of packers which consist essentially of a packing ring 40 and a pair of backer rings 90 of leather or other suitable material positioned in the groove, one of each side of the packing ring 40. The inner arcuate face 42 of the packer ring 40 makes sealing engagement with the bottom 91 of the packing ring groove 81 by the resilient grip of the ring 40 within the groove. In general practice, the inside diameter of the ring 40 is somewhat smaller than the diameter of the bottom of groove 81 and in these dimensions standard ring diameters and groove dimensions may be followed as already accepted in the trade.

The outside arcuate face 41 of ring 40 rests against the surface 35 of the bore of tubular body 12. When in position on piston 13, the outside diameter of the ring 40 is slightly greater than the bore of tubular body 12 so that a predetermined amount of squeeze is applied to the ring 4t) to effect the minimum sealing pressure of the ring 40 against both the wall 35 of the tubular body 12 and against the bottom of groove 81 in piston 13.

The backer rings 96 located on each side of the packer ring 40 are adapted to make direct contact with the bottom of groove 81 on their inner circumferential faces 92, and also to make direct contact with the surface 35 of tubular body 42 on their outer circumferential faces 93. However, backer ring 90 does not tit against either the bottom of the groove 81 nor against the surface 35 tight enough to produce a fluid-tight seal. Backer rings 90 are preferably made in one piece so that no slot will bring sharp cutting edges to bear against the packer ring 40 when it is subjected to high hydraulic pressure or to rapid motion.

The backer rings 90 on either side of packer ring 40 hold the packer ring from rotation in the groove 81 and prevent extrusion of the backer ring into the interstice between the piston 13 and cylinder 12 when under the impress of high hydraulic pressure and/or rapid motion. The axial overall width of the packer assembly which includes one packer ring 40 with two backer rings 90 is but enough less than the groove 81 to permit easy assembly.

This combination of one packer ring 40 with a backer ring 90 on each side thereof, positioned in grooves of a piston 13 which is held concentric within a cylinder 12 requires the bare minimum of squeeze on the packer' to make an effective seal over an extremely wide range of hydraulic pressures. This minimum squeeze keeps the friction against the wall 35 to a minimum and allows the easiest movement of the piston.

In some cases, it may be preferable to use only the packer ring 40 alone in a groove 81 especially dimen -sioned for it. In this case, the fiat sides of the groove 81 would bear directly against the at sides 43 and 44 of the ring 40 and hold it against rotation in the groove.

However, experience has shown us that it is'preferable touse the backer rings on either side of the packer ring 40 for best and longest service life. In a similar manner, packer ring 40 might be used in a groove 81 with only one backer ring 90 on one side of it. This prac tice also has proven less eiiicient than the use of two backer rings, one on either side of the seal ring 40 as presently illustrated in Figures 1 and 2.

In some cases, it has been found that the piston packer assembly, as shown in Figure 2, can be modified and only one of the packer assemblies used. There is no preferred choice between retaining the packerin the skirt section 61 or the head section 62 of the piston. Either assembly seems to give the same results. However, in any case, the two guide rings 82 located in the skirt section 61 and the head section 62 should be retained. The guide ring located in the head section 62 may be in part replaced by the centering action of the wiper ring 70, but this wiper ring being of relatively soft material does not hold the piston 13 in such secure alignment in the cylinder bore as does the guide ring located in the head section 62, and for that reason the use of two guide rings has been found to give most satisfactory results.

A single wiper ring 70 is shown on the lower or liquid side of the piston 13 because this is the only side of the piston from which dirt may be expected. However, if in some other arrangement dirt were to be present or possible from both sides of the piston, a second wiper ring on the other end of the piston would become of value.

While the preferred embodiment of this invention has been illustrated and described herein, the same is not to be limited to the details of construction shown and described, except as defined in the appended claims.

I claim:

1. A hydraulic packer system to hydraulically seal between two relatively reciprocatory members, which includes: a metallic cylindrical member; a metallic piston of substantially less diameter than the bore of said cylindrical member; a pair of grooves in said piston, one groove near each end of said cylinder; a second pair of grooves in said piston axially inward of said first pair of grooves; non-metallic anti-friction bearing rings in each of said first pair of grooves adapted to ride in their respective grooves on their inside surface and against the bore of said cylinder on their outside surfaces to hold said piston from contact with the bore of said cylinder and axially concentric in the bore of said cylinder; an annular sealing ring in each of said second grooves having an axially arcuate face on its inside circumference to seal against the bottom of said grooves, an axially arcuate face on its outside circumference to seal against the bore of said cylinder, and a substantially at face on each side of said body, the axial thickness of said body being less than the radial thickness thereof; and a continuous backer ring positioned on either side of said body in each of said grooves comprising a substantially at annulus having an outer circumferential face adapted to ride against the bore of said cylinder, an inner circumferential face contacting the bottom of said groove, a side of said backer ring being adapted to seat against the side of said groove, and a side of said backer being adapted to seat against a face of said body, the sides of said two backer rings and the side faces of said body in said groove being adapted to cooperate with the sides of said groove to hold said body against rotation in said groove.

2. A piston assembly adapted for relative reciprocation in a cylinder in sealing relationship therewith, which includes: a cylindrical piston provided with a plurality of axially spaced circumferential grooves; a sealing ring in an intermediate one of said grooves having an arcuate outer circumferential face, an arcuate inner circumferential face and relatively flat sides between said faces, said ring providing a fluid seal between said cylinder and said piston; continuous non-resilient relatively tat backer rings 7 on either Side vofysealing ring in said groove to support the Asame in position; and non-metallic guide rings in grooves on either side of said intermediate groove of a size and shape to maintain said piston spaced from and centralizedwithin said cylinder whereby to prevent undue compression of said sealing ring and possible direct contact between said piston and cylinder.

References Cited in the le of this patent UNITED STATES PATENTS 1,761,142 McCoy June 3, 1930 FOREIGN PATENTS France Dec. 12, 1945 

